1. Field of the Invention
The invention relates to optical amplification and free-space optical communication.
2. Discussion of the Related Art
When the cost to install a transmission cable is high, a free-space optical communication channel can offer an inexpensive alternative for a point-to-point optical communication channel. In a free-space optical communication channel, the data-carrying light beam crosses the transmission region without guiding by a transmission optical waveguide. Thus, use of a free-space optical communication channel can avoid the cost associated with installing a transmission optical fiber. The absence of such installation costs can significantly reduce the total cost of implementing a new point-to-point optical communication system.
The absence of a transmission optical fiber also reduces power transmission efficiencies in the optical communication system. In particular, the diameter of the data-carrying light beam can diverge along the free-space optical communication channel. Thus, a free-space optical communication system may deliver a lower portion of the transmitted light power than a fiber-based optical communication system having an optical communication channel of the same length.
Due to the above-described power transmission inefficiencies, free-space optical communication systems may operate quite differently than conventional fiber optical transmission systems. Often, a free-space optical communication system has a transmitter that produces a high output optical power to compensate for divergence of the data-carrying light beam.